Modern technology is currently supplying the general public and the process industries with machinery capable of operating under severe conditions. Many of these machines require lubricants having properties which are not available with the conventional greases and oils. Thus, modernization of the mechanical devices has strained the petroleum industry for the development of a second generation of lubricants capable of satisfying the lubricating requirements of the new machines.
Recently, a new grease composition has been developed containing a novel mono- or polyurea thickening agent. This grease has been found to exhibit superior endurance and high-temperature lubricating properties. The polyurea thickening agent is disclosed in U.S. Pat. Nos. 3,243,210 and 3,243,372. More recently, advances in the polyurea grease art have resulted in the formulation of an improved polyurea grease containing an alkaline earth metal carboxylate (see, for example, U.S. Pat. Nos. 3,846,314 and 3,846,315).
While this grease solves many of the problems associated with the older lubricants, it is handicapped by rusting properties. This is a typical problem associated with most multipurpose grease thickeners. Rusting is a major problem in many machines exposed to a corrosive environment. To combat the rust problems, conventional rust inhibitors have been incorporated into the greases. The conventional inhibitors, however, are quite selective for the particular grease involved and often interfere with the essential properties of the grease. For example, some inhibitors may impart satisfactory rust inhibition but only at the expense of adversely softening the grease. Conversely, some inhibitors may be quite compatible with the grease but are relatively ineffective in rust protection. Some additives have been developed which exhibit good rust inhibition, but when incorporated into a mono- or polyurea and metal carboxylate-containing grease form grit or small particulate matter in the grease. One such additive is disclosed in U.S. Pat. No. 3,868,329 which is directed to a Mannich base prepared by reacting phenol with formaldehyde and certain amines; while this additive is an effective rust inhibitor in polyurea greases, it tends to cause the formation of grit in the grease.
It is, therefore, an object of this invention to provide an improved grease composition.
It is an additional object to provide a mono- or polyurea-metal carboxylate grease composition containing a compatible rust inhibitor.
It is another object of this invention to provide a mono- or polyurea and metal carboxylate-containing grease which has improved rust inhibition and which does not contain substantial amounts of grit.
Other objects and their attendant advantages will become apparent from the following description of the invention and appended claims.